(1) Field of the Invention
The present invention relates generally to methods and devices for safely relieving excess pressures from high pressure vessels such as compressed gas cylinders. More particularly, the present invention is directed to a method and device for preventing the dangerous pressure release effects resulting from corrosion of a pressure vessel.
(2) Description of the Prior Art
A paramount concern in the use of compressed gas cylinders is the ever-present potential for rupturing of the pressure vessel wall resulting in violent and dangerous release of pressure from the vessel. Two principal physical conditions which cause the rupturing of the vessel wall are excess pressure increase within the vessel and corrosion of the vessel. The excess pressure and corrosion conditions may occur simultaneously and combine to present an unexpected and dangerous result.
A number of devices are available for venting excess pressure from an over-pressurized vessel in response to an increase of the pressure within the vessel to a pressure level above a safe limit. For example, a commonly employed pressure release device consists of a spring-loaded valve installed within an opening formed in the vessel wall. U.S. Pat. Nos. 2,380,964 and 2,951,614 disclose exemplary pressure relief mechanisms which are welded within an aperture formed in the wall of the vessel to be protected.
U.S. Pat. No. 4,347,942, assigned to the assignee of the present invention, discloses a pressure relief device which is responsive to pressure induced physical changes in the pressure vessel itself. The device is formed by coining the end wall of the vessel. The device of U.S. Pat. No. 4,347,942 is essentially self-regulating because the activation point automatically varies with vessel wall thickness. The continuing expansion of the vessel wall past a critical point causes tearing of the metal within the coined region, thus forming an aperture, and results in the venting of excess pressure from within the pressure vessel. The device of U.S. Pat. No. 4,347,942 also includes a restrictor which limits the discharge rate through the formed vessel wall aperture thereby preventing a violent release of excess pressure and a resultant propulsion of the vessel.
While the previously available relief devices have addressed the problems associated with the excess pressure build-up within the vessel, such devices are generally ineffective in addressing conditions resulting from corrosion induced rupturing of the vessel wall which rupturing may occur at vessel pressures well within safety pressure limits. Conventionally, pressure vessels are coated with paints or other special coatings to inhibit corrosion of the vessel wall. However, the conventional anti-corrosion techniques are not infallable and do not provide safety or pressure control means for dealing with the resulting effects when damaging corrosion of the vessel does occur. The present invention is directed to preventing the dangerous results presented by a corrosively induced rupture of the wall of high pressure vessels.